As many as 90% of Veterans with posttraumatic stress disorder (PTSD) report nightmares and insomnia and even when nightmares are excluded, sleep disturbances are the most prevalent symptoms of PTSD with roughly 50%-70% of patients suffering from co-occurring sleep disorders. The typical sleep complaints include nightmares, distressed awakenings, nocturnal panic attacks, sleep terrors and insomnia. While it has long been established that PTSD engenders sleep disturbances and averse clinical outcomes, current investigations indicate that disordered sleep is also a risk factor for the development of PTSD. In military personnel with combat exposure, comorbid insomnia and OSA, a condition originally labeled as ?complex insomnia? has emerged as one of the most challenging sleep disorder to manage. In the presence of PTSD, the co-occurrence of OSA and insomnia is also associated with significant morbidity. Veterans with both PTSD and complex insomnia report more psychiatric symptoms, chronic pain, and higher rates of suicide. Further, these Veterans may have more difficulty adhering to CPAP because of increased awareness of the mask due to frequent awakenings and an inability to initiate or return to sleep with the mask in place. Fortunately, there are effective treatments for each of these sleep disorders. Traditional treatment models consist of treating OSA first, followed by adjunctive or concurrent treatment for insomnia only if the response to CPAP is deemed unsatisfactory. However, the suboptimal response observed in Veterans with PTSD from such an approach in terms of quality of life, PTSD symptoms, and CPAP adherence highlights the need to examine alternative modalities of treatment. At present, there are no general guidelines on the best strategy to treat complex insomnia in Veterans with PTSD. Prior studies have shown that cognitive behavioral therapy (CBT) is effective for treating insomnia when compared with hypnotic agents. Whether combination therapy offers a therapeutic advantage over CBT alone for complex insomnia in Veterans with PTSD is yet to be determined. The objective of this proposal is to conduct a pragmatic, randomized, parallel clinical trial comparing the effectiveness of Brief Behavioral Therapy for Insomnia in Military Veterans (BBTI-MV) plus eszopiclone, a non-benzodiazepine hypnotic, versus BBTI-MV alone in 52 combat-exposed Veterans with PTSD and OSA with coexisting insomnia on global sleep quality of life, PTSD symptoms, and CPAP adherence. The topic addresses several key areas of unmet needs for Veterans with PTSD and sleep disordered breathing. Among these are: 1) the association between complex insomnia and PTSD on global sleep quality of life; and 2) the effectiveness of combined treatment of CBT and eszopiclone versus CBT alone in improving sleep quality and PTSD symptoms; and 3) the impact of each treatment regimen on CPAP adherence. By establishing the most effective therapy in alleviating insomnia that complicates the presence of OSA in Veterans with PTSD, higher CPAP adherence will ultimately translate into improved cognitive function, enhanced quality of life, and suppression of PTSD symptoms. The long term benefit of this trial will also lead to opportunities for more personalized treatment including delivery method via mobile health technologies which will allow greater assimilation of results across several domains.